sexylingual
Adj. a quality attributed to an individual who was once assumed to speak a language foreign to oneself but in turn destroys your perception of attractiveness and sheer sex appeal through an adept or even verbally acrobatic deployment of your common tongue.
"Until the measured cadence of Downton Abbey-esque English slipped from his deceptive lips, I had no idea how sexylingual the Spanish deckhand actually was, I will bear his children."